Monoclonal antibodies have been generated that are reactive with tumor associated antigens found on the surface of human breast and colon carcinoma cells (Colcher et al., Proc. Nat. Acad. Sci. 73: 3199, 1981). These antibodies may eventually prove useful in the diagnosis, prognosis, and treatment of human carcinomas. Specifically, monoclonal antibodies may be used to (a) phenotype primary carcinoma lesions as to subsequent biologic behavior, (b) aid in the detection of malignant cells in effusions and aspiration cytology, and (c) detect metastatic tumor lesions in situ via gamma scanning with radiolabeled monoclonal immunoglobulins; since not all monoclonal antibodies react to all breast or colon carcinomas, it will first be necessary to determine if the antigenic phenotype of a metastatic lesion from a given patient is similar to the antigenic phenotype of the primary lesion. The specific aims of this proposal are the use of monoclonal antibodies to tumor associated antigens and immunohistochemical techniques to determine: (1) The degree of antigenic diversity that exists between primary and metastatic breast cancer lesions of the same patient. (2) The degree of antigenic diversity that exists between primary and metastatic colon cancer lesions of the same patient. (3) If a correlation exists between the antigenic phenotype of a primary colon lesion and subsequent biologic behavior, such as (i) prognosis or (ii) metastatis to a particular site. (4) If a correlation exists between the antigenic phenotype of breast axillary lymph node metastases and the biologic behavior of the primary lesion. (5) The ability of monoclonal antibodies to differentiate benign from malignant breast lesions in fine needle aspiration biopsies in comparison with paraffin block specimens for conventional histology. (6) The usefulness of monoclonal antibodies as markers for malignancy or benignancy of cells in effusions.